Removed unused imports.
Setting event.creation_info
Using smi: scheme for origin.earth_model_id

Not sure about all this "smi:" thing, though.
azimuth and distance for secondary arrivals.
More origin.quality attributes.
Fixes for origin.creation_info

- creation_info was wrongly attributed to
  the event and not to the first origin;
- also added creation_info for origins associated
  to centroid locations.
First, preliminary test suite for mchedr.

- Based on QuakeMLTestCase();
- Still work in progress...